The invention relates to a novel method for making metal strip or sheet directly from a molten mass of the metal. From prior patents issued to King (U.S. Pat. Nos. 3,522,836 3,605,863) and others, it is known how to make strip in this manner. King discloses a method whereby a layer of the liquid metal is deposited onto the smooth, outer, cylindrical surface of a chilled roller by a so-called melt drag process. In the melt drag process the moving substrate passes through a meniscus of liquid metal delivered by an orifice and drags the metal from the orifice. The layer quickly solidifies on the chill surface and is removed as a strip.
By the above melt drag method or, so far as we know, by other methods not utilizing an orifice for delivery, the surface of metal strip formed by rapidly chilling a molten metal layer on a smooth substrate may contain various casting defects. These defects are generally a vestige of poor (thermal) contact regions of the liquid metal with the substrate. The poor contact results in slower solidification of metal than in adjacent regions of good contact.
A patent to Buxmann, et al. (U.S. Pat. No. 4,250,950) discloses a metal mold with projections for controlling the rate of metal solidification, but apparently not for improving surface finish as proposed herein.
Other methods exist for producing strip which replicates the surface of the drum (see U.S. Pat Nos. 2,561,636 and 4,212,343, for example). Such methods are not relevant to the present invention because the method produces smooth metal strip which preferably does not replicate the drum. A rather smooth finish is desired so that the strip may be formed and used as cast (such as for roof gutters, for example) or may be further formed into useful shapes with only a minimum of cold rolling.